This application claims the priority of Japanese Patent Application No. 10-244936 filed on Aug. 31, 1998, which is incorporated herein by reference.
The present invention is related to a metal V-belt used as a power transmission means in a V-belt infinite variable-speed drive and in particular to a metal V-belt that comprises metal elements.
This type of metal V-belt is already known conventionally and is comprised by an endless belt shaped metal ring and a plurality of elements supported along the metal ring. Further, this metal V-belt transmits power between a drive pulley and a driven pulley. Both of these pulleys can variably control the V channel width and by means of variably controlling this V channel width, the wrapping radius of the V-belt on both pulleys can be changed and the change gear ratio changed in infinite steps.
FIG. 8 and FIG. 9 show examples of the composition of the elements used in this type of metal V-belt. The element 30 has a front surface 31 and a rear surface 32 parallel to each other and a tapered surface 33 is formed on the lower half of the front surface 31. This tapered surface gradually changes its thickness along the rear surface 32. Further, on the left and right sides of the element 30 a ring channel 34 is formed whereon is attached a metal ring (not shown in the figure).
A V side face 35 is formed on both the left and right sides of the tapered surface 33. This V side face is supported on a slanted surface of a pulley (not shown in the figure). The boundary between the front surface 31 and the tapered surface 33 is a rocking edge 36. Each element 30 allows this rocking edge 36 to make contact with the rear surface 32 of the preceding adjacent element 30 on the pulley allowing this to lean frontward and rearward as an axis. Because of this, the V-belt can wind on the pulley. Further, a cylindrical-shaped protruding male coupling 37 is formed on the front surface 31 and a round-shaped hole female coupling 38 is formed on the rear surface 32. Both of these couplings 37, 38 are engaged and connect to each other between adjacent elements 30, 30 which in turn lines up forming one row on the metal ring.
In a metal V-belt with this type of composition, when relative slippage occurs between the elements and pulleys during the transmission of power due to clearance (space) between the elements or when the core of the metal belt shifts between the driving and driven pulleys, there is the danger of the lifespan of the V-belt being reduced because of friction between the members. There have been numerous proposals up to now for metal V-belts which implemented different element shapes in order to reduce relative slippage during the transmission of power and core shifting. Japanese Laid-open Patent Publication No.06-272737 (A) is an example of this. This example is one in which the pulley winding radius characteristics are improved and the core shifting is reduced by means of forming the lower end portion from the rocking edge of the element in a shape that becomes thinner a the end on the tapered surface and the convex circular arc-shaped surface.
Besides this, for example, Japanese Patent Publication No. 08-30517 (B) discloses a composition wherein the rocking edge is a shape that combines a circular arc-shaped surface with a large diameter and a circular arc-shaped surface with a small diameter and the adjacent element pitch on the pulleys is made smaller to reduce the relative slippage between the elements and the pulleys. Another example is Japanese Laid-open Patent Publication No.05-106691 (A) in which is disclosed a composition wherein two or more rocking edges are provided on the element to allow the essential length of the perimeter of the V-belt to change in response to the winding radius of the pulley which in turn controls the amount the core shifts to minimum levels during speed changes. An even further example is Japanese Laid-open Patent Publication No.10-47438 (A) in which is disclosed a composition wherein rocking edges are provided on both the front surface and the rear surface of the element to allow the changes in the clearance between elements due to the velocity ratio thereby controlling slippage between the V-belt and the pulleys.
However, when determining the shape of the elements of the above-mentioned metal V-belts, in particular, the radius of curvature of the convex circular arc-shaped rocking edge, the Hertzian stress acting on the rocking edge during the transmission of power was taken into account. This Hertzian stress is a parameter that affects the clearance between the elements and the opposing pitching lifespan. If this is not taken into account, there will be excessive clearance and the slippage between the pulleys and elements will grow larger and in addition there is a possibility that pitching caused by rough contact at the rocking edge may reduce the lifespan of the elements.
The object of the present invention is to provide a metal V-belt with a composition that can maintain a suitable clearance between elements.
A further object of the present invention is to provide a metal V-belt with a composition that sufficiently satisfies a performance resistant to pitching.
The metal V-belt of the present invention comprises an endless belt shaped metal ring member and a plurality of metal element members supported along the metal ring member. This V-belt transmits power between a drive pulley and a driven pulley. The metal element members have a cross-sectional convex circular arc-shaped rocking edge with an axis leaning against the opposing front and rear metal element members along with having a convex portion (for example, the male coupling 28 in the embodiment) and a concave portion (for example, the female coupling 29 in the embodiment) on the principal plane. By means of engaging the adjacent metal element members together, the convex portion and the concave portion can be lined up in a row at the front and rear on the metal element members. An allowable value of a clearance (Ct) between the total elements obtained as a sum of clearance (Cs) between the elements during a no-load stop when this metal V-belt is stretched between the drive pulley and the driven pulley and clearance (Ch) between the elements occurring due to Hertzian stress acting on the rocking edge of the metal element members while the metal V-belt is transferring power is stipulated to a value less than the protruding height (for example, height h of male coupling 28 in the embodiment) of the convex portion.
Furthermore, in the present invention, the maximum Hertzian stress ("sgr"hm ) acting on the rocking edge while the metal V-belt is transferring power is stipulated to a value less than the allowable Hertzian stress ("sgr"ho) that satisfies the opposing pitching lifespan of the metal element members. Namely, the radius of curvature R of the rocking edge is set within a range that satisfies R1xe2x89xa6Rxe2x89xa6R2 for a minimum radius of curvature R1 determined in correspondence with the maximum Hertzian stress and a maximum radius of curvature R2 determined in correspondence with an allowable value of clearance between the total elements.
If a metal V-belt with this type of composition is provided, the clearance between the elements is always maintained at a fixed gap (less than the protruding height of the convex portion). Therefore, friction between the pulleys and element can be reduced along with improving the transmission efficiency of the power. Further, the opposing pitching lifespan is always satisfied thereby improving endurance reliability. Even further, even if external disturbances, such as vibration, occur while the metal V-belt is transferring power, the linkage between the elements will not separate thereby eliminating an possibility of damage to the male-female engagement portion.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.